The demand for electronic devices is led by the products in the multimedia field, such as a mobile terminal, a game machine, and the like, and has steadily increased. The copper (Cu) damascene interconnect structure is used in such electronic devices, e.g., a part of Large-Scale Integration (LSI). The copper interconnection has a lower resistance and a higher current density than an aluminum interconnection.
In order to accommodate a need for a higher integration of LSI, it is required to provide an interconnection structure which has thinner line-widths and higher withstand current densities.
As one of approaches to improve the interconnection structure, the carbon nanotube (CNT) which has a carbon cylindrical structure with a lower resistance and a higher withstand current density has got some attention.
Because of the one-dimensional electronic characteristic due to the shape anisotropy, the electrons flow through the carbon nanotube by a ballistic conduction, and a maximum current density is approximately in the order of 109 A/cm2. The carbon nanotube is excellent in the electromigration resistance to such an extent that it can flow thousand times the current of Cu per unit area.
Japanese Patent Application Publication Nos. 2006-120730-A and 2006-202942-A, IEEE International Interconnect Technology Conference 2006, p. 230, IEEE International Interconnect Technology Conference 2005, p. 234, and Jan. J. Appl. Phys. Vol. 41 (2002) pp. 4370-4374, for example, disclose that the CNT is used as interconnection structure in the LSI.
Japanese Patent Application Publication No. 2006-120730, and IEEE International Interconnect Technology Conference 2006, p. 230 disclose that a bundle of carbon nanotubes extended vertically from a bottom surface of a hole in an insulating film is used as via interconnection.
FIGS. 4A to 4C show conventional steps of forming a via made of carbon nanotubes.
First, as shown in FIG. 4A, a tantalum (Ta) film 102 is formed on a copper film 101 as a copper diffusion barrier, and then a film, e.g., a titanium nitride (TiN) film 103, which sets a growth direction of the carbon nanotubes is formed thereon.
Then, a silicon oxide film 104 is formed on the TiN film 103, and then a via hole 105 is formed by patterning the silicon oxide film 104 by means of the photolithography method, or the like. Then, cobalt (Co) catalyst particles 106 are formed on a surface of the TiN film 103 through the via hole 105 to distribute uniformly in the surface.
Then, as shown in FIG. 4B, carbon nanotubes 107 are formed upwardly from the Co catalyst particles 106 in the via hole 105 in predetermined condition.
Then, as shown in FIG. 4C, portions of the carbon nanotubes 107 protruding from an upper surface of the silicon oxide film 104 are removed. Thus, the carbon nanotubes 107 left in the via hole 105 are used as the via.
A diameter of the carbon nanotube 107 is almost in a range of subnano to several tens nm, and a length of the carbon nanotube can be grown up to several hundreds μm.